cosmogenic

The argument goes like this: When cosmic rays hit the atmosphere, they not only form the cosmogenic nuclides, they also form ions, which give rise (through complicated and as yet poorly known ways) to cloud-condensation nuclei.

Cosmic rays also generate the so-called cosmogenic nuclides.

The most widely used cosmogenic isotope for absolute dating is carbon - 14, which is exchanged with living organisms as 14 CO 2.